The present invention relates generally to the field of metering devices, and in particular, to electrical utility revenue meters.
Electrical utility revenue meters, or simply revenue meters, are devices that, among other things, measure electrical energy consumed by a residence, factory, commercial establishment or other such facility. Electrical utilities rely on revenue meters for many purposes, including billing customers and tracking demand for electrical power. A common form of revenue meter comprises an inductive drive that rotates a spinning disk at an angular velocity proportional to the amount of power being consumed. The spinning disk drives mechanical counters that provided an indication of power consumed over time.
Over recent years, electronic meters have been developed that are replacing the spinning disk meter design in several applications. Electronic meters use electronic circuits to measure, quantify and display energy consumption information. In general, electronic meters may be divided into two portions, a sensor portion and a measurement portion. The sensor portion includes sensor devices that are connected to the electrical system of a facility, and more particularly, to the power lines. The sensor devices generate signals that are indicative of the voltage and current in the power lines. In general, the sensor portion of a revenue meter operates with the high voltages and currents that are present on the power lines.
The measurement portion of an electronic meter uses the signals generated by the sensor portion to determine watt-hours, VA, VAR and other information that quantifies the power consumed by the facility. The measurement portion typically also includes a display for displaying the power consumption information. In contrast to the sensor portion, the measurement circuit works with reduced or attenuated voltage and current signals that are compatible with electronic devices, and in particular, digital electronic devices.
Occasionally, revenue meters can malfunction or suffer damage through external forces and require repair or replacement. Repair or replacement of many commonly-used revenue meters presently require an interruption in the electrical power to the facility being metered. In general, power service interruptions are extremely undesirable from the electrical utilities' perspective because they reduce customer satisfaction. Accordingly, there exists a need for a revenue meter that may be repaired or replaced without interrupting power service to the facility being metered.
Another problem that has arisen due to the advent of electronic meters pertains to service upgrades. In general, electronic meters offer a wide variety of features that are facilitated by digital electronics. These features may include power demand monitoring, communications, and power line and meter diagnostics. Because these feature are facilitated by the digital circuitry in the measurement portion of the meter, the services or functions available in an electronic-type revenue meter may be altered by replacing digital circuit components in the measurement portion of the meter.
For example, consider a utility that installs several electronic meters without power demand monitoring because it is deemed unnecessary at the time of installation. A year later that utility may determine that it would be desirable to have the power demand monitoring capability in those meter installations. The installed electronic meters may, in theory, be upgraded to provide that capability typically by replacing portions of the electronic portion. The sensor portion components would not need to be replaced.
As a practical matter, however, it is often more convenient to replace the entire meter rather than the individual digital circuit components. Accordingly, enhancement of the capabilities of the metering often requires replacement of the entire meter. Replacement of the entire meter, however, undesirably creates waste by forcing the replacement of relatively costly, and perfectly operable, sensor components.
A meter introduced by Asea Bover & Brown ("ABB") addresses this concern by providing a modular meter that includes a sensor portion and a removable measurement portion. The measurement portion may be removed from the sensor module and replaced with another measurement portion having enhanced functionality. The ABB meter, however, has significant drawbacks. For example, the measurement portion of the ABB meter can not be replaced while the sensor portion is connected to an electrical system of a facility because removal of the measurement portion would expose extremely dangerous voltages and currents to a human operator or technician. Thus, although the modular design allows for upgrades, the power to the facility must nevertheless be interrupted to perform such upgrades for safety purposes.
A further problem with the ABB meter arises from its bulkiness. The sensor portion of the ABB meter is enclosed in housing and the measurement portion is enclosed in another housing. Both housings include large areas of unused space that increase the bulkiness of the meter. The bulkiness undesirably increases costs in shipping and storing of the meters both as assembled or in their modular components.
There exists a need, therefore, for a modular meter having modular components that may be removed or replaced without interruption to the electrical power service to the facility to which the meter is connected. There is also a need for a revenue meter having reduced bulkiness.